PLASMA POLYMERIZATION OF HEXAFLUOROPROPYLENE - FILM DEPOSITION AND STRUCTURE

Thin, pinhole-free, highly adhering films for advanced technology applications can be deposited through plasma polymerization, a low temperature, solvent-free process. This research studies the influence of plasma environment (power, pressure, and monomer mass flow rate (F-m)) on the plasma polymerization of hexafluoropropylene (HFP) using a common industrial parallel-plate plasma reactor. The deposition and structure of the transparent, yellow, and highly adhering plasma polymerized HFP (PPHFP) film are investigated. The rate of polymerization (R(p)) increases with power (W) and reaches a plateau when the plasma changes from energy starved to monomer starved while the rate of etching (R(e)) continues to increase. The rate of deposition (R(d)), the difference between R(p) and R(e), increases with W, reaches a maximum, and then decreases. In a monomer starved plasma R(d) increases with F-m or pressure through a more efficient utilization of the energy supplied at a given W or even at a given W/F-m. The abstraction of F and the preferential scission of the C - CF3 bond can explain the F/C ratio of 1.5, the significant amount of double bonds, and the relative lack of CF3 in a PPHFP that consists of CF3, CF2, and CF groups. A gas phase dominated polymerization produces submicrometer particles some of which agglomerate into spheres. Both the particles and the spheres deposit on the surface and are incorporated into the film with further polymerization. (C) 1995 John Wiley and Sons, Inc.